1. Field of the Invention
This invention relates to a vehicle navigation system which displays a pattern (font) screen, an enlarged intersection screen, etc., without using an image signal line such as RGB, NTSC etc.
2. Description of the Prior Art
Prior art navigation systems, in general, have an image memory (VRAM) provided in a main unit side for providing guidance and displays of a map of the vicinity of the vehicle position or the destination by sending guide map data and road map data to a display in RGB or NTSC format.
FIG. 15 shows an example of such a navigation system including a main unit 50 for generating data necessary for the navigation system and a display 60 for displaying a guidance image. Upon start-up, the main unit 50 reads a program stored in a ROM 51 into a RAM 52 and reads out map data and road data, etc., stored in a CD-ROM in a CD-ROM driver 53. Present position is detected by a GPS receiver 54 or a gyro sensor 55 and a route to a destination is searched by a CPU 56. The CPU 56 reads a vehicle signal and sequentially generates image data for route guidance. The generated image data is read sequentially into a special purpose image memory (VRAM) 58, from which it is read out by a image controller 57, then converted in an encoder into an image signal 59, and finally sent as an image signal in a format such as RGB, NTSC, PAL, SECAM, VGA, etc. This image signal is decoded in a decoder 62 and is displayed on a display 60 as the guidance image through a driving circuit 61.
Navigation systems using a LCD display, with characters and fonts on the display side, without VRAM on the main unit side, transmitting image pattern numbers, etc., from the main unit side, which display a traveling direction arrow, etc., are also known. FIG. 16A exemplifies such a navigation system in which font (pattern) data is stored in advance in a memory 53 on the display side. The font data consists of plural data patterns for arrows, etc. assigned numbers as shown in FIG. 16B. Referring to FIG. 16A, in performing route guidance, a main unit 50 of the navigation system transfers a predetermined font pattern such as No. 1, No. 2, etc., over to the display side which then reads out data received in the received font patterns, and the data read out is displayed on a display 51 by the driving circuit 52.
A vehicle navigation system transmits image data as shown in in NTSC format, etc. and displays guidance. Accordingly, enormous amounts of image data must be transmitted. Therefore, a special purpose system such as an image controller, an image memory, etc., are required, with the result that the system price has become higher. Further, not only the main unit of the navigation system but also the display side requires a decoding circuit for image signals, which also results in increasing the system price.
Further, if drawing is performed by using pattern (font) data for a display, representation of the display is limited to a number of patterns (fonts), which must therefore represent only simple display, and, accordingly, actual road shape, a detailed enlarged intersection image, etc., can not be displayed. It is also difficult to store the shape of all intersections in font and any increase in the shape patterns to be displayed requires memory space on the display side to be extended, which also results in increasing the system price. Furthermore, the display unit must be a special purpose display in order to receive the font data, which also results in increasing the system price. Further, to increase the patterns (fonts), the main unit must be replaced along with the display with which it is paired, again resulting in an increase in the system price.